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andrewoliv avatar image
andrewoliv asked

Decreasing input voltage during bulk charge

I have an old 30' sailboat with a primary lead acid battery bank and a 55 amp alternator. This primary bank is used to start the engine and as house batteries. They are deep cycle lead acid batteries. I recently installed a lithium bank with a Orion TR Smart Isolated 12V 30 Amp DCDC charger. The lithium bank is primarily used to power a portable refrigerator. I also installed a BMV 712 Smart battery meter.

I notice during bulk charge while the engine is running there are 25-29 Amps being provided by the charger and the input voltage for the lead acid bank/Alternator drops (as expected).

However, sometimes. the input drops as low as 9 volts (Input voltage for the DC DC Charger from the lead acid bank/Alternator).

Is this normal or am I degrading the lead acid batteries somehow? or is there an alternator issue? should I consider switching to AGMs or upgrading the alternator?


Thanks in advance!

orion-tr smartdc-dc charger
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pwfarnell answered ·

Is this the actual battery voltage as measured on the battery terminals or as measured at the DC to DC charger. If it is at the DC to DC charger then when it is this low check the actual battery voltage. If it is at the batteries then they are being seriously abused and this may be because of an alternator problem or it could be due to a poor wiring contact, crimp, undersized wiring or an isolator switch with a high resistance. If it is just at the DC to DC charger then it is likely to be just a poor wiring contact, crimp, undersized wiring or an isolator switch with a high resistance.

The thing with the 30A Dc to DC charger is that the 30A is the output current, the input current is higher than this, perhaps 35A so it is pulling a significant load on your alternator and the cable sizes have to be set for this currently flow and low voltage drop as the Orion has to work harder the lower the incoming voltage.

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andrewoliv avatar image andrewoliv commented ·
Thank You. I rechecked the wire gauge and I am using 8G which is a little over 3mm. Suggested in the installation guide is 6mm at 1/2 a meter distance and 10mm at a meter so that may be the first issue. I'll change that immediately. I chose the wire gauge based on the biggest that would fit into the Orion. Not sure how 6mm or larger is gonna fit. But ill try
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kevgermany avatar image kevgermany ♦♦ andrewoliv commented ·
Metric wire sizes are cross section in mm2, not diameter. 6mm2 wire is about 3mm conductor diameter.
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